The signals that govern blood vessel formation in both normal and disease states are similar and have been conserved throughout vertebrate evolution. This enables the use of a genetically tractable animal model, such as the zebrafish, to dissect and analyze these signals. We have found that vascular endothelial growth factor (VEGF) is required specifically for the formation of arteries and the differentiation of arterial endothelial cells in zebrafish. Since VEGF has become a target for therapeutic manipulation of blood vessels in human diseases, it is clinically relevant to better understand the mechanism by which VEGF drives artery development. Our work demonstrates a role for phospholipase C gamma-1 (Plcg1) during VEGF-mediated artery development and suggests that other signals also converge on Plcg1 to drive this process. In this proposal, we will identify molecules that interact with Plcg1 during artery development by first identifying domains in Plcg1 that are required for artery development through in vivo structure/function analysis. Based on these results, we will identify molecules that interact with Plcg1 and determine their function during artery development. We will also identify new zebrafish mutants that affect VEGF and Plcg1 signaling during artery development. For this purpose we will perform a genetic screen using transgenic zebrafish with fluorescently labeled blood vessels that allow easy identification of mutant phenotypes. Finally, we will characterize segmental artery mutant phenotypes and identify candidate genes responsible for these phenotypes. These studies integrate traditional biochemical techniques with the powerful genetic tools available through the use of the zebrafish system and will provide a comprehensive approach to better understand how Vegf and Plcg1 govern artery development. Since these signaling mechanisms are evolutionary conserved, the molecules we identify in this proposal represent possible targets for clinical manipulation of pathological blood vessel formation.